Elevator control system



y 6, 1969 0. A. KRAUER ET AL 3,442,352

ELEVATOR CONTROL SYSTEM Filed Oct. 15, 1965 Sheet 0: WI DR S FIGURES vy/ F 1 5 a4 I Y CW m F2 L1 2E F-O h LL! (1') g l g F I 6 INVENTORS OTTO ALBERT KRAUER O ss Time(sec.) SIDNEY HOWARD BENJAMIN BY ?.W ATTORNEY y 6, 1969 Q. A. KRAUER ET AL 3,442,352

ELEVATOR CONTROL SY STEM Filed Oct. 13, 1965 Sheet 2 of 4 VOLTAGE VELOCITY 'rt/sec.

0 IO 20 5O 4O 5O 6O 70 O 90 I00 HO INVENTORS Distro floor in ft OTTO ALBERT KRAUER 7 SIDNEY HOWARD BENJAMIN BYf'ZW- y/ ATTORNEY May 6, 1969 Filed Oct. 13, 1965 O. A. KRAUER ELEVATOR CONTROL SYSTEM IL 2 DRK scc J( f m N; @L- Q 0M 92 2 56 5 g 7'8 3\4 62 sec DRK FIG. 3 2 7/8 DRK' 8 FIG. H

g l Time(sec) g 2 FR O T T2 T314 T5 1' INVENTORS OTTO ALBERT KRAUER SIDNEY HOWARD BENJAMIN BY f'flf ATTORNEY May 6, 1969 o. A. KRAUER ET AL 3,442,352

ELEVATOR CONTROL SYSTEM Filed Oct. 13, 1965 Sheet 4 of 4 VS Q/RHI 72 L J RHZ VS I EH4 VT RH5 32 ft/sec.

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| SPDS I sPDs 2 Y'WZFIGURES |,2,3) VS FIGURE 8) INVENTORS OTTO ALBERT KRAUER SIDNEY HOWARD BENJAMIN BYE/52% ATTORNEY United States Patent 3,442,352 ELEVATOR CONTROL SYSTEM Otto Albert Krauer, Tuclrahoe, and Sidney Howard Benjamin, Brooklyn, N.Y., assignors to Otis Elevator Company, New York, N.Y., a corporation of New Jersey Filed Oct. 13, 1965, Ser. No. 495,585 Int. Cl. B66b 1/06 US. Cl. 187-29 15 Claims ABSTRACT OF THE DISCLOSURE A high performance servo control system particularly suited for controlling the speed of a motor which acts on a variety of loads, such as the direct current hoisting motor of a high speed passenger elevator system. Means are provided for comparing control signals from speed dictating equipment with feedback signals to insure fidelity and stability of performance. The feedback signals include signals proportional to the speed of the motor and to the higher derivatives of that speed with respect to time. These signals are derived from a motor speed indicating device in the form of a tachometer generator driven by the motor armature and from a network con nected to the motor armature circuit in a configuration which substantially simulates the interacting energy storage properties of the impedance of the motor armature and of the moving masses of the system when the motor is acting on a predetermined one of its various loads.

This is an invention in the art of elevator control. In its broadest aspects it relates to elevator control systems in general; specifically, it is concerned with controlling hoisting motors in high speed passenger elevator systems.

Part of the subject matter disclosed in this application is being claimed in the divisional application of Otto Albert Krauer, Kenneth Raymond Brooks and Sidney Howard Benjamin, Ser. No. 740,667 filed June 27, 1968 entitled Elevator Control System and assigned to the assignee of this application.

In elevator systems in which hoisting motors drive traction sheaves to raise and lower the cars, the velocity at which the cars ascend and descend is controlled by controlling the operation of the hoisting motors. In some of these systems, especially those in which the cars transport passengers at high speeds, it is desirable that the hoisting motors be controlled in a manner which accelerates the cars from rest to a maximum running speed and decelerates them from that speed to a stop in a minimum period of time. It is important, however, that this control be exercised without discomforting the passengers. As a result, it is essential that those factors which can cause discomfort, the acceleration, the deceleration, and the jerk, i.e. the rate of change of acceleration and deceleration, be limited in magnitude. In past systems this has been attempted by confining changes in the speed of the elevator hoisting motor to discrete steps calculated to prevent excessive jerk and excessive rates of change of speed. High speed elevators, however, require a large number of such steps and for each of these steps it is likely that a field adjustment is necessary.

It is an object of this invention to control the operation of an elevator hoisting motor in such an improved manner that variations which are introduced in the speed of the motor, take place in a continuous stepless fashion. As a result, the discrete changes in motor speed which have been perceptible to the passengers riding in elevator cars of prior systems are eliminated, and a further object of the invention, to improve the comfort of passengers, is achieved.

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It is a still further object of this invention to provide an elevator control system in which the majority of adjustments can be made during manufacture so that the field adjustments are reduced to a minimum.

A preferred embodiment of the invention features a high performance closed loop system which operates an elevator hoisting motor in accordance with control signals it receives from speed dictating equipment. Means are provided in the system to feed back signals from a motor speed indicating device and from a network connected to the motor armature circuit in a configuration which substantially simulates the interacting energy storage properties of the moving masses of the elevator systern and the impedance of the hoisting motor armature. These feedback signals are combined with the control signals received from the speed dictating equipment to insure that the motor accurately follows the control signals and that the system operates in a stabilized manner.

In the accompanying drawing:

FIGURE 1 is a schematic representation of an elevator control system embodying the invention;

FIGURE 2 is a schematic representation of an alternative elevator control system embodying the invention;

FIGURE 3 is a more detailed schematic representation of a part of the control systems shown in FIGURES 1 and 2;

FIGURE 4 is a simplified schematic wiring diagram in across the line form of the coils of some of the switches whose contacts are shown in FIGURE 3;

FIGURES 5 and 6 are graphs on which time is represented by the abscissa and voltage by the ordinate;

FIGURE 7 is a graph on which distance is represented by the abscissa and both velocity and voltage by the ordinate;

FIGURE 8 is a simplified schematic circuit diagram of equipment employed by the elevator control systems shown in FIGURES 1 and 2;

FIGURE 9 is a graph on which distance is represented by the abscissa and both velocity and voltage by the ordinate;

FIGURE 10 is a more detailed schematic representation of a selector machine used in the control systems shown in FIGURES 1 and 2;

FIGURE 11 is a graph on which time is represented by the abscissa and velocity by the ordinate.

The accompanying drawing will now be described so that what is schematically represented therein may be identified in connection with the reference characters by which it is designated.

In FIGURE 1 the rotating element or armature 10 of a direct current elevator hoisting motor is illustrated. Mounted on the shaft of armature 10 for rotation thereby, is a traction sheave TS for the hoist ropes 11 of an elevator car CA and its counterweight CW. An electromechanical brake ER is provided to be applied to a brake drum mounted on the shaft of armature 10 in any satisfactory well known manner. Main field 14 of the elevator hoisting motor is connected across a constant potential source schematically represented by battery 15. In accordance with the well known Ward Leonard principles of variable voltage control, motor armature 10 is connected across the output of a direct current generator whose armature 16 is mounted on the same shaft as rotor 18 of an alternating current drive motor, not otherwise shown. Main field 20 of the direct current generator is connected in series with resistor RDG between the center tap of the secondary of transformer 23 and the output circuit from the silicon controlled rectifiers of reversible single phase full wave rectifying circuit 22. The input connections to circuit 22 are across the secondary of transformer 23 by way of lines S1 and S2. The primary of transformer 23 is connected across a source of single phase 60 cycle alternating current indicated by lines 01 and 02. This same source is also connected to the input circuit of control device 24, which may suitably take the form of a magnetic amplifier. The output circuit of device 24 is connected to the gates of the silicon controlled rectifiers of circuit 22 to transmit firing pulses to these gates under conditions to be more fully explained later. Another input circuit to device 24 is provided from driving amplifier 26. Connected to the input of driving amplifier 26 is summation network 28, which may suitably include a static element operational amplifier. Of the two input circuits to network 28, one is connected in a degenerative feedback arrangement from generator field 20 and the other is coupled to summation network 30 through an RC. stabilizing phase lag network 32 which symbolizes various passive networks those skilled in the art employ as suitable in different applications. Summation network 30, which also may suitably include a static element operational amplifier, is arranged with three input circuits. The first of these is connected to equipment mentioned below, the second to the ouput circuit of a tachometer generator 34 mounted on the shaft of motor armature 10, and the third to a feedback network 36 connected to the circuit of motor armature 10.

The equipment connected to the first input circuit of network 30 includes comparator-switch 38, function generator 40 and selector machine 42. Equipment suitable to implement selector machine 42 is fully disclosed subsequently. Comparator-switch 38 includes a differential relay having two coils DRFG and DRSE, making contacts DR 1-2 and breaking contacts DR 3-4. Function generator 40, shown in more detail in FIGURES 3 and 4, comprises two phase motor 50 having control winding 52 and reference winding 54 typically connected across a three phase supply of alternating current indicated by lines G1, G2, G3 and neutral N. Variable voltage transformers 56 and 58 are connected through contacts of delay reversing switch DRG across control winding 52 and reference winding 54 to permit different voltages to be applied across the windings in response to the operation of switch DRK. Connected directly to the shaft of motor 50 for rotation thereby is disc 61 of eddy current brake device 62 comprising said disc and solenoid 64. Through gear box 66 there is also connected to the shaft of motor 50, sliding contact BR1 of linear potentiometer POTl and cams lLC, 2LC, 3LC and 4LC which operate associated limit switches 1LS, 2LS, 3LS and 4LS. One end of potentiometer POTl is connected to ground whereas the other end is connected through contacts of direction reversing switch DGU to a source of positive and negative potential. Various other circuits for the coils of electromagnetic switches are shown in FIGURE 4. These switches enable the desired operation of motor 50 and their operation will be explained in greater detail later. They are designated as follows:

DRK--Delay Reversing Switch DRKXAuxiliary Delay Reversing Switch FSR-Floor Stop Relay 1LFirst Limit Switch Relay 2LSecond Limit Switch Relay 3LThird Limit Switch Relay SCC-Stop Control Switch STE-Dictation Start Switch In FIGURE 2 an arrangement similar to that of FIG- URE 1 is shown. In this arrangement the Ward Leonard control equipment of FIGURE 1 has been replaced by static element adjustable voltage power converting equipment 44. Resistor RDGF provides a degenerative feedback arrangement for this equipment which may suitably include a three phase full wave silicon controlled rectifier reversible bridge circuit arranged to provide a reversible polarity, adjustable magnitude direct current output from a three phase alternating current supply indicated by lines T1, T2, T3. Subject to the counter EMF of armature 10, the magnitude and polarity of this output current are determined by the sequence and the phase relationship by and at which the silicon controlled rectifiers are fired and the period of each cycle of each phase of the alternating current supply during which the silicon controlled rectifiers conduct. These factors, in turn, are determined by the magnitude and polarity of the output signal from summation network 30. Equipment satisfying these operating requirements can be purchased from the General Electric Company and may include the regulator amplifier, the gate pulse generator and amplifier, and the silicon controlled rectifier bridge circuit of the power conversion equipment sold by that company under the trade name Silcomatic.

FIGURE 8 shows computing circuitry including input circuits V and V carrying signals from selector machine 42 and tachometer generator-34, respectively. These, together with circuits carrying constant signals, are connected to up and down direction differential amplifiers 72 and 74 whose outputs are connected to various NOR elements N1, N2, N3 and N4. The output circuit from these NOR elements is connected to relay driver amplifier 76 which is used to operate auxiliary stop control switch SCCX through the energization of its coil.

FIGURE 10 shows a schematic representation of a well known selector machine designated SM from which extends a shaft 694. Connected to this shaft are a plurality of gear boxes XBI, XB2 and X83. Switches FS'D and SPDS are connected to shaft 694 through gear box X81 and sliding contacts BRIO and BRll of potentiometers POT 10 and POT 11 are connected to shaft 694 through gear boxes XB2 and X133, respectively. The center of each potentiometer POT 10 and POT 11 is grounded. Their ends are connected to positive and negative voltage supplies marked V1+ and V1 for potentiorneter POT 10 and V2-]- and V2 for potentiometer POT 11.

FIGURES 5, 6, 7, 9 and ll show various graphs which have already been identified. The curves on these graphs Will now be described in general but it should be understood that their full significance will appear hereinafter. It should be noted, at this point, that some of the graphs have only voltage ordinates while others have both velocity and voltage ordinates. A scale is shown on FIGURES 7 and 9 for each of the ordinates representing velocity to aid in understanding the specific operation which is described. No voltage scale is shown on the graphs having voltage ordinates since such a scale is peculiarly a matter of choice and design in relation to the specific equipment used for particular elements of the control system. Two of the graphs have distance abscissas. Each of these is scaled for the same reason that the forementioned velocity ordinates are sealed. The abscissas of the other three graphs are time. These, as well as, the velocity ordinate of FIGURE 11, are not scaled since the durations of the functions shown by the curves on these graphs depend upon the length of particular runs made by an elevator car controlled in the specific manner described. Certain points of time, however, thought helpful to un derstanding the described operation, are included.

The curve shown in FIGURE 5 represents an input signal, which the elevator control systems shown in FIG- URES 1 and 2 are to follow so that they operate in accordance with certain speed characteristics. This signal is represented as a function of time for a portion of a full speed run of an elevator car controlled by these systems.

FIGURE 6 shows a curve which represents a similar function of time as that on FIGURE 5 except it is for a portion of a less than full speed run of an elevator car.

Plotted on FIGURE 7 are two curves A and B. With respect to the ordinate representing velocity, each curve represents a particular velocity as a continuous function of a cars distance from a selected floor at which it is to stop in a prescribed manner. Cunve A represents the velocity at which an elevator car undergoing a constant acceleration should be traveling when it starts to decrease its acceleration upon receiving a signal to stop at the fioor selected. Curve B represents the velocity at which an elevator car undergoing a certain deceleration should be traveling if it is to stop at the selected floor in the prescribed manner. With respect to the ordinate representing voltage, curve B represents the manner in which the potential of an input signal varies as a function of the distance an elevator car is from a selected floor at which it is to stop. This signal, if applied to the elevator control systems of FIGURES l and 2, stops the car at the selected floor in the prescribed manner.

Plotted on the graph of FIGURE 9 are two curves B and C. Curve B on this graph is a portion of curve B of FIGURE 7 in an enlarged scale and represents the same functions as it represents there. Curve C, with respect to the ordinate representing velocity, represents the velocity at which an elevator car should be traveling within one to two feet of a selected floor if it is to stop at the fioor in a desired manner. With respect to the ordinate representing voltage, curve C represents the manner in which the potential of an input signal varies as a function of a cars distance within one to two feet of a selected floor at which it is to stop. This signal, if applied to the elevator control systems of FIGURES l and 2 stops the car at the selected floor in the desired manner.

The curve plotted on FIGURE ll represents velocity characteristics as a function of the time during a typical run of an elevator car operated in a prescribed manner.

In order to fully appreciate the invention it is helpful to understand some practical aspects concerning the operation of high speed elevator cars. According to one prescribed method of operation, an elevator car is to be started from rest with a rate of change of acceleration of 8 ft./sec. which is to last until an acceleration of 4 ft./sec. is attained. The car is then to be accelerated at a constant acceleration of 4 ft./sec. until it reaches a velocity from which a decreasing acceleration at the rate of 8 ft./sec. brings its acceleration to zero and its velocity to its full rated value. When this full rated velocity is reached the car is to continue at that velocity until it receives a signal to stop. It is then to be slowed down at a rate of change of deceleration of 8 ft./sec. until a deceleration of 4 ft./-sec. is attained. The car is then to decelerate at a constant deceleration at 4 ft./'sec. until it reaches a velocity from which a decreasing deceleration at the rate of 8 ft./sec. brings it to rest.

The foregoing assumes the car travels a sufficient dis tance to attain full rated speed before receiving a signal to stop. Under actual operating conditions a car often receives a signal to stop during the period of constant acceleration. In that case, upon the signal to Stop being received the acceleration is to be decreased at the rate of 8 ft./sec. until it is zero whereupon the car is then to be slowed down at a rate of change of deceleration of 8 ft./sec. This is to continue until a deceleration of 4 ft./sec. is reached. Thereupon the car is to be brought to rest in the same way it would be if it had run at full rated speed.

The foregoing method of operation is possible if the speed of the car is controlled solely as a function of time. This type of control, however, is not entirely suitable because it does not insure that the car is within an acceptable distance of a floor level when it is brought to rest. For this reason, in the system to be described, part of the decelerating operation is controlled by the distance the car is from the fioor level at which it is to stop. This control is initiated when the car starts to decelerate at 4 ft./sec. and is continued until the car comes to rest. At the time it is initiated the speed of the car is so coordinated with its distance from the floor at which it is to stop that its scribed method is introduced. This is done because a signal which provides the prescribed method of operation may afiect the stability of the system as it brings the car closer to the floor. For this reason, the signal which is employed in the last foot of travel into a floor varies the operation slightly from that prescribed yet it brings the car into the floor rapidly and accurately regardless of the load on the car and without affecting the stability of the system. With the foregoing as background, operation of an embodiment of the invention will now be presented.

Assume the elevator system including the equipment illustrated in FIGURE 1 receives, in any well known manner, a signal to start to move in a selected direction of travel. As the doors close, the car is enabled to move and function generator 40, in a manner hereinafter to be described, begins to generate a signal whose potential with respect to time takes the form of the curve shown in FIGURE 5. (Of course, it is understood that if the car is to move in the opposite direction of travel the output signal of function generator 40 is of a form whose curve is opposite in polarity but symmetrical to that of FIG- URE 5.) Consider separately the effect this generated signal has on the elevator system. For reasons later described, the signal travels unaffected from function generator 40 by way of line W1 through contacts DR 3-4 of comparator-switch 38 into summation network 30. It is received by network and passes through that piece of equipment to RC. lag network 32. Summation network 28 receives an output signal from network 32 and passes it to driving amplifier 26. It is there amplified and transmitted to control device 24 where it causes gate pulses to be generated for the silicon control rectifiers of circuit 22. As these gate pulses are generated the direct current generator of the motor generator set is excited by a rectified current which starts to flow from circuit 22 through main field 20. A signal proportional to this current is fed back to network 28 through resistor R effectively to eliminate the time constant of main field 20 according to well known principles of feedback control. At the same time the excitation in the generator develops a voltage across generator armature 16 which causes a current to fiow through armature 10 of the elevator hoisting motor. As a result the motor begins to run and the elevator car starts to move in the selected direction of travel.

It is to be understood that the magnitude and polarity of the amplified signal received by control device 24 in response to the output signal from network 30 determines the time at which gate pulses are generated during each cycle of the alternating current supply applied to circuit 22 between lines S1 and $2. This governs the interval of each cycle of the alternating current supply during which the silicon control rectifiers of circuit 22 conduct. In this way the output signal from network 30 regulates the magnitude and the polarity of the current flowing through main field 20 and controls the output voltage of the direct current generator and the speed of the elevator hoisting motor.

Under the assumed conditions, the output signal from network 30 is controlled by that of function generator whereby a current flows in armature 10 of the hoisting motor which for reasons to be hereinafter described, starts the car with a rate of change of acceleration of 8 ft./sec. The potential of the output signal of function generator 40 then increases to a maximum value as a function of time as shown in FIGURE 5 which brings the car to its full rated speed in accordance with the prescribed method of operation.

Function generator 40 continues to generate a signal which maintains the car at full rated speed until the system receives a signal to stop. At that time, illustrated in FIG- URE 5 as time 1 the output signal of function generator 40 starts to decrease causing the armature voltage of the direct current generator to decrease. As a result, the current in armature of the hoisting motor is altered in such a way that the car starts to decelerate. As will later be more fully described this continues until an output signal from selector machine 42 becomes substantially equal in magnitude to that of function generator 40. At that time comparator-switch 38 opens contacts DR34 to disconnect the function generator from network 30 and closes contacts DR12 to connect the selector machine thereto. A signal is thereafter transmitted from selector machine 42 by Way of line W2 through contacts DR12 to network 30 to bring the car to rest within an acceptable distance of the floor at which it is to stop in the described desirable manner. The potential of this signal varies as a function of the cars distance from the floor at which it will stop in a manner to be hereinafter described. As previously mentioned a selector machine capable of generating a signal of this nature is fully disclosed subsequent- 1y.

Throughout the operation of this system tachometer generator 34 is driven by armature 10 and produces a signal whose potential is proportional to the speed of armature 10 and elevator car CA. This signal is fed back through resistor R to summation network 30 wherein the conventional feedback technique it is combined with the dictated speed signal transmitted through comparatorswitch 38 to provide a differential or error signal which insures that the hoisting motor is rotating at the speed being dictated to it. This arrangement is stabilized by feeding back, in a manner to be immediately described, signals representing the higher derivatives of the speed. Thus signals representing acceleration and rate of change of acceleration or deceleration and rate of change of deceleration, as the case may be, are also fed back to summation network 30 to regulate the differential or error signal.

The manner in which these stabilizing signals are derived will be apparent from the following description.

It is well known that motor armature 10 and the masses it drives, including such members as elevator car CA and its counterweight CW, are accelerated and decelerated, as the case may be, by a component of the current which flows in motor armature 10. For convenience, this component will be hereinafter referred to as the acceleration component. In addition to the acceleration component, under conditions in which the load in the car does not balance the amount by which the counterweight outweighs the empty car, the armature current contains another component which acts to support the unbalanced portion of the heavier of the two members to prevent it from descending undesirably. This latter, or load, component, of course, varies as the load on the car varies and at the balancing load its magnitude is zero. What is more, in order to produce the same modes of acceleration and deceleration regardless of the load in the elevator car, the acceleration component of the armature current also varies as the load in the car varies from the balancing load.

Neglecting frictional losses, the current that fiows in motor armature 10 under balanced load conditions contains no load component and is proportional to the acceleration or deceleration, as the case may be, of armature 10. The magnitude of this current depends on the resistance in the motor armature, the inductance in the motor armature, and the inertia of both the motor armature and the masses it drives at balanced load. These components of resistance, inductance and mass comprise an electro-rnechanical system which is mathematically definable by a second order differential equation. An electrical analogue of this second order electromechanical system at balanced load is itself mathematically definable by a second order differential equation. One such analogue is an RLC circuit wherein R the resistance in the motor armature, L=the low frequency inductance in the motor arumturc,

and

C=the electrical capacitance equivalent to the mechanical inertia of the motor armature and the masses it drives at balanced load.

The magnitude of the capacitance in this analogue circuit is well known to be the quotient of the total moment of inertia of both the motor armature and the masses it drives at balanced load with respect to the motor shaft divided by the product of two of the motor constants, one being the torque per ampere and the other the electromotive force per radian of revolution. The magnitude of the inductance in this circuit is determinable by conducting a low frequency response test to obtain a Bode plot of an open loop system including the hoisting motor. The magnitude of the inductive reactance of the motor armature is equal to the magnitude of the analogous capacitive reactance of this tested system at the corner frequency determined by the test. Thus once the magnitude of the analogous capacitance and the corner frequency are known, the magnitude of the low frequency inductance in the armature can be determined. The magnitude of the inductive component of the analogue RLC circuit of the forernentioned electro-mechanical system is equal to the inductance determined in this manner. The magnitude of the resistance component of the analogue RLC circuit, of course, is equal to the measured motor armature resistance.

Feedback network 36 includes components of resistance R and R inductance L and capacitance C whose values preferably are so proportionate to the corresponding resistance, inductance and capacitance values of the electrical analogue described above, that under balanced load conditions the current flowing through network 36 is substantially a synchronized miniature reproduction of the current through motor armature 10 and under such conditions is proportional to the acceleration and deceleration of direct current motor armature 10. Moreover, the current through network 36 is independent of the different steadystate magnitudes of the load component of the current through armature 10 and varies in synchronism with variations in its acceleration component. By means of a tap on resistor R a signal proportional to the current through network 36 is fed back to summation network 30 through resistor R to provide the desired stabilizing feedback signal of acceleration and deceleration.

The desired feedback signal of rate of change of acceieration and deceleration is readily provided in the system by feeding back a signal proportional to the rate of change of the current in feedback network 36 through isolating amplifier or buffer 37 by way of capacitance C connected in parallel With resistance R The scale which is selected for the miniature reproduction which network 36 produces fixes the proportionality factor relating the magnitudes of the components of the network to the magnitudes of the corresponding components of the analogue RLC circuit. The proportionality constant between the respective capacitances is the inverse of the proportionality constant between the respective resistances and inductances so that the product of the capacitance and inductance and the product of the capacitance and resistance of network 36 are equal to the respective products of the corresponding components of the analogue RLC circuit. Similarly, network 36 can be synthesized by networks of other configurations. Each of these synthesized networks would be defined by a transfer function (i.e., a mathematical equation relating to the behavior of the networks output to its input) which is of the same form as and proportional to that of the analogue RLC circuit so that each such transfer function would have individual terms proportionately corresponding to those terms of the transfer function of the analogue RLC circuit which are determined by its resistance, inductance and capacitance.

Before proceeding with more specific details of some of the individual elements heretofore mentioned, the embodiment illustrated in FIGURE 2 will be described. For this purpose, assume now that the elevator system including the equipment shown in FIGURE 2 receives, in any well known manner, a signal to start to move. As described in relation to the operation of the equipment of FIGURE 1, function generator 40 begins to generate a signal of the nature of that shown in FIGURE which passes through comparator-switch 38, summation network 30 and lag network 32. The signal passing through network 32 is applied to static element power converting equipment 44 wherein it causes that equipment to produce an output voltage which is applied across armature of the elevator drive motor. The forward gain of equipment 44 is such that the magnitude of the signals received by it at the outset of operation causes a current to flow through armature 10 which accelerates the elevator car according to the heretofore prescribed method of operation.

If the car is permitted to run a sufficient distance before receiving a signal to stop, this system operates to bring the car to full rated speed and to rest again in the manner described for the system of FIGURE 1. In view of that fact and of the similarity between the equipment of FIGURE 1 and that of FIGURE 2, it is not believed necessary to present a description of operation of the equipment of FIGURE 2 during a full speed run. In order to present a full description of an elevator system including the invention, however, a run of less than full speed will be described. Because the equipment of FIGURE 1 has been previously described in detail, a less than full speed run will be described with reference to FIGURE 2. It should be understood, however, that just as the equipment of FIGURE 2 operates in a manner similar to that of FIGURE 1 for a full speed run, so does that of FIGURE I operate in a manner similar to that of FIGURE 2 for a less than full speed run.

Assume now that the car associated with the equipment of FIGURE 2 has been started as described but that before it reaches full rated speed and while it is accelerating at a constant acceleration of 4 ft./sec. it receives a signal to stop. At that time, illustrated in FIG- URE 6 as time 1 the output signal of function generator 40 ceases to follow the linear shape of the curve of FIGURE 5 and conforms to the shape of FIGURE 6. As the signal of this latter shape is applied to the system it causes equipment 44 to change the current flowing through armature 10 at a rate whereby the acceleration of the car is decreased at the rate of 8 ft./sec. This continues for one half second in accordance with the prescribed method of operation until the car is no longer being accelerated. At that time the output signal of function generator 40 decreases and when applied to equipment 44 causes it to change the current flowing through armature 10 so that the car starts to slow down, The output signal of function generator 40 continues to decrease to further slow down the car until, for the reason given in the description of operation of the equipment shown in FIGURE 1, comparator-switch 38 switches the input connection of network from function generator to selector machine 42. The car is thereafter brought to a stop in the same manner as described in relation to the operation of the equipment of FIGURE 1.

In the system of FIGURE 2 as in that of FIGURE 1 a feedback signal representative of speed is transmitted to summation network 30 from tachometer generator 34 to produce an error signal which insures that motor armature 10 is operating at the speed dictated by the signals from function generator 40 and a selector machine 42. Also, feedback signals are transmitted to summation amplifier 30 from the circuit of armature 10 through network 36, buffer 37, resistor R and condenser C to stabilize the system. Again it is preferred that the magnitudes of the components of feedback network 36 be such that the current through it under conditions of balanced load is proportional to the current which causes the acceleration of motor armature 10 under such conditions.

It is to be understood, of course, that there may be circumstances in which it is desirable to stabilize individual systems of the types shown in either FIGURE 1 or FIGURE 2 other than by feeding back currents through circuits whose components are of magnitudes determined as heretofore mentioned. In each circumstances the method by which to proceed is initially to connect a circuit containing components so determined into the system in the manner shown so that the system may operate in a stabilized condition. The elevator car can then be run and the magnitudes of these components adjusted until the system operates in the manner desired. Thus, for example, it has been found more satisfactory in one embodiment of the invention to have the magnitude of capacitance C more closely represent the inertia of armature 10 and the masses it drives when the load on the car is midway between balanced load and full load as opposed to having it represent the inertia at balanced load.

A high degree of fidelity is imposed upon both the system shown in FIGURE 1 and that shown in FIGURE 2 in following the dictated speed signals from function generator 40 and selector 42. In tested embodiments of these systems satisfactory fidelity has been obtained by operating with a system loop gain of between the tachometer feedback signals to network 30 and the output signals from network 30 measured with the loop open, for instance, at the junction between resistor R and network 31).

Heretofore it has been mentioned that, upon the elevator car being enabled to run, function generator 40 generates a signal whose potential with respect to time takes the form of the curve shown in FIGURE 5. It has also been mentioned that, when a signal to stop is received before the car reaches full rated speed and while it is accelerating at 4 ft./sec. function generator 40 generates a signal whose potential with respect to time ceases to follow the curve of FIGURE 5 and conforms to the shape of that of FIGURE 6. An embodiment of a function generator which operates in the foregoing manner together with an embodiment of comparator-switch 38 and that of mechanisms which operate to generate signals to stop will now be thoroughly described for two separate runs of an elevator car. The first description follows immediately and explains the operation of this equipment during a full speed run, the other appears later and explains its operation during a less than full speed run.

Assume the elevator car of the system of either FIG- URE l or FIGURE 2 is set to travel in a selected direction and that accordingly contacts DGU 12 (FIGURE 3) of a direction reversing switch DGU, not otherwise shown, are closed and contacts DGU 3-4 of the same switch are open. In addition, assume that cams :1LC, 3LC and 4LC (FIGURE 3) are engaging switches ILS, 3L8 and 4LS so that contacts lLSl, 3LS1 and 4LS1 are closed, and that a sufficient potential exists between lines L1 and L2 of FIGURE 4 to energize the illustrated coils when their circuits are completed. Also assume that a signal to start has been given and that the car starts to close its doors to enable it to run. As the doors close, selector 42, which will hereinafter be described, starts to scan in the direction in which the car is to travel in order to select the next floor at which a stop is to be made. For this purpose, the scanning mechanism of selector 42 moves to a position in advance of the position of the car as indicated by the selector. This movement is such that during scanning the distance advanced in terms of hoistway distance is always greater than the distance required to bring the car to a stop at a selected floor in the manner desired. Also, while its scanning mechanism is in an advanced poistion selector 42 generates a signal representing the distance advanced. At this time it is believed to be more suitable to a coherent description simply to state that such a signal is generated, rather than to interrupt the present description to describe the signal and the reason why it is generated. Consequently, both the signal and the purpose served by it will be fully detailed at subsequent and more appropriate points in the description.

As it is generated, the signal from selector 42 is transmitted to coil DRSE (FIGURE 3) of the differential relay of comparator-switch 38. During the accelerating period of a run and until a hereinafter explained moment during the decelerating period, the signal generated by selector 42 is greater in magnitude than the output signal from function generator 40. For this reason, during this time coil DRSE of the differential relay receives more excitation from selector 42 than coil DRFG receives from sliding contact BR1 of potentiometer POTI of function generator 40. As a result throughout this period, contacts DR 1-2 of the differential relay are Open and contacts DR -3-4 of that relay are closed and the output of function generator 40 is transmitted to summation network 30 as hereinbefore described.

As selector 42 starts to scan contacts ADVLl (FIG- URE 4) open and interrupt the circuit for the coil of floor stop relay FSR, releasing that relay to open its contacts :FSR 1-2 and close its contacts FSR 3-4. The opening of contacts FSR 1-2 interrupts the circuit for the coil of stop control switch SCC which releases but without effect upon the system at this time. Contacts F SR 3-4, however, close to energize the coil of delay reversing switch DRK through closed contacts DRKX '1-2. Switch DRK thereby operates to open its contacts DRK 5-6, DRK 7-8 and DRK 9-10 and to close its contacts DRK 3-4 all without effect at this time. Contacts DRK 1-2, however, are closed by the operation of switch DRK to energize reference winding 54 of motor 50 from the line to neutral voltage across lines G3 and N of the three phase supply.

After contacts ADVLl open, contacts ADVL2 (FIG- URE 4) engage. When this happens, the coil of dictation start switch STB is energized through closed contacts 4LS1 of the fourth limit switch and switch STB operates to open its contacts STB 1-2. This interrupts the circuit for the coil of first limit switch relay 1L, releasing that relay to open contacts 1L 3-4 and IL 5-6 and to close contacts 1L 1-2. Contacts 1L 3-4 and IL 5-6 open without effect at this time. Contacts 1L 1-2, however, close to apply the line to line voltage across lines G1 and G2 of the three phase supply to control winding 52 of motor 50 through closed contacts DRK 3-4, SCC 1-2, 1L 1-2 and SCC 3-4. Motor 50 starts to rotate and by design accelerates substantially linearly to its running speed in one half second. As a result, the output signal from sliding contact BR1 of linear potentiometer POTI increases during this period in the parabolic form shown between points and A of the curve of FIGURE and the car starts with a rate of change of acceleration of 8 ft./sec. in the manner previously explained. Thereafter since motor 50 has reached a constant running speed the output signal from sliding contact BR1 increases linearly with time as shown in FIGURE 5 to accelerate the car constantly at 4 ft./sec. The rotation of motor 50 during this time causes cams lLC, 3LC and 4LC to disengage switches lLS, 3LS and 4LS which as a result open their contacts 1LS1, 3LS1 and 4LS1. Also cam 2LC engages switch 2L5 to cause it to close its contacts 2LS1. Contacts 1LS1 open without effect but contacts 3LS1 and 4LS1 open to deenergize the coils of third limit switch relay 3L and dictation start switch STB, respectively. Each of these in turn releases to close its respective contacts 3L 1-2 and STB 1-2 without effect. Contacts 2LS1 close to prepare the energizing circuit for the coil of second limit switch relay 2L.

Motor 50 continues to rotate at constant speed until cam 1LC reengages first limit switch 11.8 to close again contacts lLSl. This completes the circuit for the coil of first limit switch relay 1L which thereupon operates to open contacts 1L 1-2 and close contacts 1L 3-4 and 1L 5-6. Contacts 1L 5-6 close without effect at this time. Contacts 1L 1-2 open to interrupt the circuit for control winding 52 of motor to deenergize that winding. Contacts 1L 3-4, in closing, complete a circuit through contacts 3L 1-2 to energize the coil of solenoid 64. The deenergization of control winding 52 causes motor 50 to start to slowdown. At the same time the energization of the coil of solenoid 64 caused eddy currents to flow in disc 61 and applies a drag braking force to the motor. In this way motor 50 is caused to decelerate substantially linearly and to come to rest in one half second. During this period the output signal from sliding contact BR1 of potentiometer POTl increases in the parabolic form shown between points B and C of the curve of FIGURE 5 to a maximum potential. This causes the cars acceleration to decrease at a rate of change of 8 ft./sec. until the car reaches full rated speed. Thereafter motor 50 remains in the position in which it came to rest to maintain the output signal of sliding contact BR1 at the maximum value shown in FIGURE 5 so that the car continues to run at full rated speed until it receives a signal to stop.

Assume now that selector machine 42 selects a floor at which it is desired to stop the car and stops its scanning operation. As this happens, contacts ADVLI and ADVL2 (FIGURE 4) close and open respectively, without effect at this time. In these circumstances, the elevator car is approaching the selected floor at full speed. At some time during this approach, the car reaches a distance from the floor which has been calculated to be required to slow down the car and bring it to rest in the prescribed manner. When this distance is reached, the selector machine operates full speed distance switch FSD to engage contacts FSDI to complete the energization circuit for the coil of floor stop relay FSR (FIGURE 4) through closed contacts SCCX 5-6, 1L 5-6 and ADVLI. Relay FSR operates to close its contacts FSR 1-2 and to open its contacts FSR 3-4. Contacts FSR 3-4 open to interrupt the circuit for the coil of delay reversing switch DRK which thereby releases to open its contacts DRK 1-2 and DRK 3-4 and close its contacts DRK 5-6, DRK 7-8 and DRK 9-10. The closing of contacts DRK 9-10 has no effect at this time. Contacts DRK 1-2 open and contacts DRK 7-8 close to energize reference winding 54 through variable voltage transformer 58 with less than the full potential of the line to neutral voltage across lines G3 to N. Contacts DRK 3-4 open and contacts DRK 5-6 close to prepare a circuit for control winding 52 to receive less than the full potential of the line to line voltage across lines G1 and G2 through variable voltage transformer 56. The closing of contacts FSR 1-2 completes the circuit for the coil of stop control switch SCC. Switch SCC thereby operates to open contacts SCC 1-2 and SCC 3-4 and to close contacts SCC 5-6, SCC 7-8 and SCC 9-10. Contacts SCC 1-2 and SCC 3-4 open and contacts SCC 5-6 and SCC 7-8 close in preparation for the reversal of the connection of the line to line voltage across lines G1-G2 to control winding 52. Contacts SCC 9-10 close to complete the energizing circuit for the coil of second limit switch relay 2L through closed contacts 2LS1. Relay 2L operates to engage contacts 2L 1-2, 2L 3-4 and 2L 5-6. The engagement of contacts 2L 3-4 and 2L 5-6 have no effect upon the system at this time. Contacts 2L 1-2 complete the circuit for control winding 52 through variable voltage transformer 56 and contacts DRK 5-6, SCC 5-6 and SCC 7-8 causing motor 50 to start to rotate in the direction opposite to that in which it last moved.

According to the prescribed operation motor 50 should be accelerated substantially linearly to its full speed in the opposite direction in one half second so that the output signal from sliding contact BR1 would decrease in a manner which would cause motor armature 10 (FIGURE 1 or 2) to start to slow down the car at a rate of change of deceleration of 8 ft./sec. In a tested embodiment, however, it has been found that a smooth and more positive transition to distance control is insured if the slowdown of the car is started with a rate of change of deceleration slightly less than 8 ft./sec. For this reason, as slowdown is initiated, the energization of reference winding 54 and control winding 52 is reduced from the full potential of their applied voltages and solenoid 64 of eddy current brake 62 is maintained energized. It takes motor 50, therefore more than one half second to accelerate to a constant running speed in the opposite direction and, as a result, the output signal from sliding contact BR1 decreases in such a manner as to cause motor armature 10 (FIGURE 1 or 2) to start to slow down the car at a rate of change of deceleration of slightly less than 8 ft./sec. The portion of the curve of FIGURE 5 shown after time r represents the output signal from sliding contact BR1 during this period.

It should be understood that after selector machine 42 selects a floor at which a stop is to be made and stops scanning, the distance between the location of its scanning mechanism at a position indicative of the selected floor and the location of the car as indicated by the selector decreases as the distance the car is from the level of the selected floor decreases. Accordingly, the generated output signal from selector 42 decreases. With respect to the ordinate voltage scale of FIGURE 7, curve B illustrated the manner in which the potential of this signal decreases as a function of the distance the car is from the level of the selected floor until the car is within approximately one foot of that level. At some distance from the floor, the potential of the decreasing output signal from selector 42 equals the potential of the output signal from function generator 40. Preferably, the manner in which the output signal from selector 42 decreases is such that this equality exists at approximately the time the output signal from function generator 40 is at point D of FIGURE 5. When both signals are equal, the output signal from sliding contact BR1 of potentiometer POT1 of function generator 40 excites coil DRFG (FIGURE 3) of the differential relay of comparatorswitch 38 as much as the output signal from the selector machine 42 excites coil DRSE. At that time the differential relay operates to open contacts DR34 and close contacts DR1-2. This disconnects the output of function generator 40 from the input circuit of summation network 30 and connects the output of selector machine 42 thereto. Network 30 thereafter receives the output signal from selector machine 42. As will be explained, this signal is designed so that it slows the car down at a constant deceleration of 4 ft./sec. in accordance with the prescribed operation.

As previously mentioned at a distance of approximately one foot from a floor level at which a car is to stop, it is desired that the output signal from selector machine 42 vary the cars operation, from that prescribed. As has been stated, this variation takes place in a manner consistent with stability which accurately brings the car to the fioor as rapidly as comfort permits regardless of load. Furthermore, this same signal from selector 42 insures that as long as the system is connected such that selector 42 provides its output signal to network 30, the car is maintained level with the floor to which it is brought even though passenger transfers may cause contraction and expansion of the hoist ropes. This has been provided satisfactorily in a tested embodiment by varying the output signal from selector machine 42 with respect to distance so that the potential of this signal and the velocity dictated by it both vary between a floor level and approximately one foot distance therefrom according to curve C shown in FIGURE 9. A comparison on the voltage ordinate scale of this curve with the portion of curve B of FIGURE 7 shown in enlarged scale in FIGURE 9 shows that for any distance from the floor between approximately one foot and two feet the ordinates of curves B and C coincide substantially. By so matching these curves a smooth transition from the prescribed method of operation to that desired with this system is insured.

Thus, as the car arrives approximately one foot from the level of the floor at which it is to stop the output signal of selector machine 42 ceases to follow curve B of FIGURE 7 and conforms to curve C of FIGURE 9. As desired, this signal rapidly brings the car the remainder of the distance into the floor and insures that after the car has stopped it will stay level with the floor without oscillating thereabout should the expansion and contraction of the ropes caused by passenger transfers tend to change its position with respect to the floor.

While the foregoing slowdown is taking place and after selector 42 is connected to summation network 30, it should be understood that motor 50 continues to rotate at a reduced speed against the force of eddy current brake 61. This causes cam lLC to disengage first limit switch 1LS to open contacts 1LS1 and interrupt the circuit for the coil of first limit switch relay 1L. Relay 1L releases to open its contacts 1L 3-4 and 1L5-6 and to close its contacts 1L 1-2 without effecting the system. In addition, cam 4LC engages fourth limit switch 4LS to close contacts 4LS1, also without effect at this time because contacts ADVLZ have been opened since selector machine 42 stopped scanning. Motor 50, therefore, continues to drive contact BR1 toward its original position against the force of brake 61 until cam 3LC reengages third limit switch 3LS and causes contacts 3LS1 to close. This completes the circuit for the coil of third limit switch 3L causing it to operate to open its contacts 3L 1-2. When this happens, the circuit for the coil of solenoid 64 is interrupted and the drag braking force of eddy current brake 61 is removed. By the removal of the drag braking force of eddy current brake 62, motor 50 is free to drive sliding contact BR1 rapidly toward its original position on potentiometer POTI in preparation for the next trip of the car. Just prior to contact BR1 arriving at its original position cam 2LC disengages second limit switch ZLS to open contacts 2LS1 and cam lLC engages first limit switch lLS to close contacts 1LS1 in preparation for the next trip of the car. This interrupts the circuit for the coil of second limit switch relay 2L and completes the circuit for the coil of first limit switch relay 1L causing contacts 2L 1-2 and IL 1-2 to open. In opening, contacts 2L 1-2 and 1L 1-2 interrupt the circuit for reference winding 52 and motor 50 coasts to a stop. Punction generator 40 is now prepared for the next trip of the car.

In the operation in the immediately preceding description, the car ran a sufficient distance to enable it to reach full rated speed before a signal to stop was received. It has been mentioned previously that a less than full speed run would also be described. The description of such an operation now follows.

It will be recalled that as the car is set to travel in a selected direction, direction reversing switch DGU operates to open contacts DGU 3-4 and close contacts DGU 1-2 but that before the car starts to move and as the doors close, selector 42 starts to scan in the direction in which the car is to travel in order to select the next floor at which a stop is to be made. It will also be recalled that after selector 42 starts to scan, motor 50 starts to rotate and function generator 40 generates a signal which starts to accelerate the car in the prescribed manner. As previously explained, after motor 50 starts to rotate, cams lLC thru 4LC operates their respective switches 1LS thru 4L5. As a result contacts 1LS1, 3LS1 and 4LS1 open and contacts 2LS1 close.

Assume now that selector 42 selects a floor at which it is desired to stop the car and stops its scanning operation. Also assume that the floor is not a sutficient distance beyond the floor from which the car starts its travel to permit it to reach full rated speed. In these circumstances the stopping operation of the car is initiated by a signal to stop which is received while the car is accelerating at a constant acceleration of 4 ft./sec. As previously mentioned, passenger comfort can be assured throughout this operation by initiating the stop when the velocity of the car and its distance from the selected floor are such that the acceleration of the car can be decreased at a rate of change of 8 ft./sec. for one half second until the acceleration ceases, whereupon the car can be slowed down at a rate of change of deceleration of slightly less than 8 ft./sec. When a deceleration of 4 ft./sec. is attained the car can be brought to a stop in accordan e with the hereinbefore described desired operation.

At the time a signal to stop initiates this desired stopping operation during a cars constant acceleration period, a relationship exists between the instantaneous velocity of the car and its distance from the selected floor at which it is to stop. This relationship is readily determinable from straightforward mathematics and is graphically illustrated in FIGURE 7 with respect to the ordinate velocity scale by the curve marked A. From this, it should be understood that the signal to stop is to be generated whenever the instantaneous velocity of the car and the distance remaining to the selected floor level at this instant both satisfy coordinates on this curve. It is now appropriate to examine how and by what means it is determined when to generate this stopping signal.

As will be recalled from the prior description of the full speed run, curve B of FIGURE 7 represents the manner in which the potential of the output signal from selector 42 decreases after floor selection. As explained, it decreases in this manner as the distance the car is from a selected floor decreases, until the car is Within approximately one foot of the floor selected. From this prior description, it should also be understood that whenever a car is more than one foot from a selected floor, the output signal from selector 42 represents the velocity at which a car should be traveling during its constant deceleration period if it is to stop at the selected floor in the manner desired. In addition, it should be appreciated that after selector 42 has selected a floor and, until the car is within approximately one foot of the floor selected the decreasing output signal from selector 42 represents this constant deceleration velocity as a function of the distance the elevator car is from the floor selected. For this reason, at distances greater than one foot, curve B, represents this velocity plotted on the ordinate velocity scale of FIGURE 7.

It is to be remembered, of course, that, when selector 42 selects a floor during a less than full speed run, the elevator car is not undergoing constant deceleration but rather is experiencing constant acceleration. Thus, to insure passenger comfort, the car must first go through a transition from constant acceleration to a decelerating condition before the output signal from selector 42 can be employed to control the speed of the car. This is accomplished by generating the signal to stop after floor selection when the car velocity and its distance from the selected floor satisfy coordinates of curve A on FIGURE 7. As has been explained, the coordinates of this curve represent the velocity a car undergoing constant acceleration can attain for its distance from a selected floor at the time a signal to stop is generated. This velocity it should be understood is the maximum velocity the car can attain for its distance from a selected floor before its acceleration must start to decrease. At that velocity and distance, a relationship exists between that velocity as represented by the coordinates of curve A and the velocity at that distance for a car undergoing constant deceleration as represented by the coordinates of curve B. This relationship is defined by the equation:

V =the constant deceleration velocity represented by the 16 selector output signal after the selection of a floor at which a stop is to be made V =the constant acceleration velocity of the car represented by the tachometer generator output signal In other words, after a floor has been selected, the signal to stop is to be given whenever the velocity of the car and the velocity represented by the output signal from the selector bear the relationship to each other defined by the above equation. For present purposes, however, and for car speeds of interest i.e. from 3.75 ft./sec. to about 27 ft./ sec. it has been found satisfactory to generate the signal to stop when these velocities bear a less complex relationship to each other. This relationship is defined by the equation V =1.04V +3.2 ft./sec. 2

A device which computes the existence of this latter equalty and generates a signal to stop as a result is shown in FIGURE 8.

In order to understand the operation of the equipment shown in FIGURE 8, the description of the less than full speed run will now be continued. It will be recalled that the car is set for a selected direction of travel and that contacts DGU 1-2 are closed. This causes a false, or binary zero (0), signal to appear at input DGU (FIGURE 8) of NOR circuit N1. It will also be recalled that selector 42 has stopped its scanning and has selected a floor at which it is desired to stop. This operated to cause a false signal to appear at input ADVL (FIGURE 8) of NOR circuit N 4.

The position of the scanning mechanism of selector 42 in advance of the location of the car causes the selector to generate an output signal which is transmitted to inputs V (FIGURE 8) of the up and the down differential amplifiers 72 and 74. Assume now that the selected direction of travel of the car is the up direction. Also assume that in such circumstances, the output signal from selector 42 is positive in polarity and that from tachometer generator 34 (FIGURES 1 and 2), appearing at inputs V (FIGURE 8) of differential amplifiers 72 and 74, is negative. For the opposite direction of travel, of course, both polarities are reversed. As a result of the polarization of these signals, the equation used in computing the existence of the proper conditions for generating the signal to stop is implemented for both directions of travel as shown in FIGURE 8.

As the acceleration of the car continues, the magnitude of the output signal from tachometer generator 34 increases. During the same period the car is getting nearer the floor which the scanning mechanism has selected and as a result the magnitude of the output signal from selector 42 is decreasing. By setting rheostats RHl and RH2 (FIGURE 8) at the proper resistance values the scales of volts per unit of velocity for the input signals from tachometer generator 34 and selector machine 42 are placed in the relationship of 1.04 to 1 with respect to each other. Thus, when the car reaches that distance from the floor at which the signal to stop should be given as previously explained, the input signal to up differential amplifier 72 from selector 42, is equal in magnitude to the input signal to amplifier 72 from tachometer generator 34 plus the input signal representing minus 3.2 ft./sec. Under such conditions, the sum of the inputs to amplifier 72 is zero volts causing it to produce a false signal at input L12 of NOR circuit N1. This makes both inputs to this circuit false and causes it to produce a true, or binary one (1), signal at its input to NOR circuit N3. As a result NOR circuit N3 produces a false output signal which appears at input L14 of NOR circuit N4. Both inputs to circuit N4 being false, it produces a true, or binary one (1), signal. This is applied to relay driver amplifier 76 to produce a signal which causes the coil of auxiliary 17 stop control switch SCCX to be energized through the circuit of closed contacts FSR 5-6 and 1L 7-8 to supply L15. Switch SCCX thereby operates to open contacts SCCX 3-4 (FIGURE 4) and close contacts SCCX 1-2 (FIGURE 4). In opening, contacts SCCX 3-4 interrupt the circuit for the coil of auxiliary delay reversing switch DRKX and condenser CDRKX starts to discharge through that coil and resistor RDRKX. In the meantime, the closing of contacts SCCX 1-2 energizes the coil of stop control switch SCC which operates to open its contacts SCC 1-2 and SCC 3-4 and to close its contacts SCC 5-6, SCC 7-8 and SCC 9-10. The opening of contacts SCC 1-2 and SCC 3-4 and the closing of contacts SCC 5-6 and SCC 7-8 reverse the connection of the line to line voltage applied across lines G1-G2 to control winding 52. Contacts SCC 9-10 close to complete the energizing circuit for the coil of second limit switch relay 2L through closed contacts 2LS1. Relay 2L operates to engage contacts 2L 3-4 to energize the coil of solenoid 64 of eddy current brake 62 through contacts 3L 1-2, which previously were closed as a result of the opening of con-: tacts 3LS1. Because of the inertia of motor 50, the reversal of the connection of the energizing source to control winding 52 does not cause motor 50 to reverse its direction of rotation immediately. It does, however, start to slow down. At the same time the energization of the coil of solenoid 64 causes eddy currents to flow in disc 61 and applies a drag braking force to the motor. In this way motor 50, by design is caused to decelerate substantially linearly and to come to rest in one half second. During this period the output signal from sliding contact BR1 of potentiometer POTl increases in the parabolic form shown between points B and C of the curve of FIG- URE 6. This causes the cars acceleration to decrease at a rate of change of 8 ft./sec. until the acceleration is zero. When this occurs condenser CDRKX is discharged sufficiently to release auxiliary delay reversing switch DRKX to open its contacts DRKX 1-2. This interrupts the circuit for the coil of delay reversing switch DRK and releases that switch to open contacts DRK 1-2 and DRK 3-4 and close contacts DRK 5-6, DRK 7-8 and DRK 9-10. In closing, contacts DRK 9-10 provide an additional path for the energizing current for the coil of solenoid 64. Contacts DRK 1-2, DRK 3-4, DRK 5-6 and DRK 7-8 operate to connect control winding 52 and reference winding 54 across lines G1, G2, G3 and N through variable voltage transformers 56 and 58 and thereby reduce their energizing potential from the three phase supply. Motor 50, after coming to rest, reverses its direction of rotation, and the reduced energizing potential causes it to take more than one-half second to accelerate to a constant running speed in the reverse direction. As a result the output signal from sliding contact BR1 decreases in the manner shown between points C and D of FIGURE 6 so as to cause the car to start to slow down at a rate of change of deceleration of slightly less than 8 ft./sec. At approximately the time that the output signal from function generator 40 is at point D of FIGURE 6 a smooth transition to distance control occurs through the operation of comparator-switch 38 and the car is brought into the fioor in the same manner as heretofore described for a full speed run. After this transition occurs, motor 50 is operated to return sliding contact BR1 to its original position preparatory to the next trip of the car, also in the same manner as previously described.

Description of selector machine suitable for use with the systems FIGURE 1 and FIGURE 2 As previously explained, selector machine 42 is a device which scans the floors in advance of the car to select the next fioor at which the car is to stop. In addition, for purposes heretofore mentioned this device generates four signals. A first signal which commences when the selector starts its scanning operation and ceases when the selector stops scanning. The source of this signal has previously been designated by contacts ADVLI (FIGURE 4). A second signal which commences and ceases shortly after the first signal commences and ceases. Contacts ADVLZ (FIGURE 4) have previously been designated as the source of this signal. A third signal which exists whenever the car is full speed stopping distance or less from a floor at which it is to stop. The source of this signal has previously been designated by contacts FSDI (FIGURE 4). A fourth signal which is a continuous indication of the distance the scanning mechanism is in advance of the indicated position of the car.

There are known devices which generate these signals. One which may be used with the present invention is the device described in United States Patent No. 2,306,817, issued Dec. 29, 1942, to D. C. Larson. In employing this device, the first signal may be generated by breaking contacts (i.e. contacts which disengage and engage when the coil of the switch which operates them is energized and deenergized, respectively) of the first auxiliary stopping relay A; the second signal, by making contacts (i.e. contacts which engage and disengage when the coil of the switch which operates them is energized and deenergized, respectively) of the second auxiliary stopping relay B; the third signal, by switch 162 if it is set to close when the car is full speed stopping distance from a floor at which it is to stop; and the fourth signal, by the angular position of shaft 694.

Another device suitable to generate these signals is disclosed in the copending application of Otto Albert Krauer et al., Ser. No. 495,446, filed concurrently herewith, for Elevator Control System, and assigned to the same assignee as is the instant application. For present purposes, however, assume the device disclosed in the foremenlioned Larson patent is employed for use with the systems of the present invention.

It is appropriate, at this time, to consider how selector 42 transduces the angular position of shaft 694 into a signal suitable to perform the functions previously attributed to it. As will be recalled, at distances greater than one foot, this signal corresponds to curve B of FIGURES 7 and 9. From FIGURE 10 it can be seen that shaft 694 drives sliding contacts BR10 and BR11 of potentiometers POT 10 and POT 11 through suitable gearing. The voltages at sliding contacts BRIO and BR11 are each a function of the distance between the scanning mechanism of selector 42 and the indicated position of the car. From previous explanations it will be appreciated that after fioor selection, it is desired that these voltages, although functions of distance, each have a form which will dictate the described operation as if each were a function of time. The following describes how this is achieved.

It has been stated that the curve of FIGURE 11 represents the velocity characteristics for a typical run of an elevator car operated in the prescribed manner. Consider this curve in the region from its origin to point A. In this region, according to the prescribed operation, the jerk, j, is constant and equal to 8 ft./sec. Assuming that the car starts from a first landing at 1:0 and that distance is measured from this landing, the following relationships can be derived by straightforward mathematics.

Jerk=j=8 ft./sec. (4) Acceleration=a=8t (5) Velocity=v:4f (6) Distance:s=4/3 (7) Velocity=v=(6s)2/3 (8) This portion of the curve extends until time 1 at which time:

a=4 ft./sec. t /z second v: 1 ft./ sec. s: ,6 foot Now, consider the portion of the curve from point A to point B, where 11:4 ft./sec. Starting with the initial conditions that at s=% foot, v=l ft./sec. it can be shown Because the curve of FIGURE 11 is symmetrical, the

above expressions, although derived for the portion of the curve between its origin and point B, are equally applicable for the prescribed method of operation to the portion of the curve from t to 1 if we regard the distance s as zero at 1 and increasing to the left toward Curve B of FIGURES 7 and 9 are a graph of Equations 8 and 9 showing the prescribed velocity during deceleration as a function of distance from a selected floor. The portion above s=% foot is a plot of Equation 9. In order to generate a signal indicative of this velocity the potentiometer POT10 (FIGURE 10) is made non-linear on each side of its center tap in accordance with Equation 9. Such a potentiometer may be made by well known techniques, starting with a linear potentiometer with many taps and adding suitable shunts. Voltages of opposite polarities V1+, V1- are applied to the extremities and the center tap is grounded. Therefore, the output voltage from sliding contact BR10 indicates, by its polarity, whether the car is above or below a selected landing, and represents, by its magnitude, the velocity at which the car should be traveling during its constant deceleration period at any distance from a selected floor, if it is to stop in the prescribed manner. Of course, the magnitude of voltages V1+, V1 are sufiicient to extend the magnitude of the output voltage from contact BR10 to and beyond that indicative of the full speed stopping distance. It should be also understood that potentiometer POT10 is suitable to provide the prescribed operation only at distances greater than A; foot from the landing and, furthermore, as has been explained, that that operation is desirable only at distances greater than about one foot.

The portion of curve B of FIGURE 9 below foot has a slope which becomes infinite as the distance from the fioor approaches zero. If a signal were to be generated in accordance with this curve, it would dictate a very large change in velocity for a very small change in distance. Systems like those of FIGURES I and 2 which could follow such a signal in the region near zero would be required to have substantially infinite gain. This, of course, is not feasible. Additionally, as the gain of these systems is increased, problems of stability increase. These considerations impose a practical upper limit on the slope of the velocity versus distance curve in the region closer than foot from a selected floor.

It must be remembered that the elevator car is not only to stop accurately at a landing but is also to stay level with a landing should expansion and contraction of the hoist ropes caused by passanger transfers tend to change the position of the car with respect to a landing. Such operations require that a signal of reasonable magnitude be generated when the car is within a region of a few inches on either side of a landing level. For this reason, a practical lower limit is imposed on the slope of the velocity versus distance curve in this region.

For the above reasons, curve B is replaced, in the region near zero distance, with curve C of FIGURE 9. This curve is derived by first determining reasonable minimum and maximum slopes based on the foregoing considerations of gain, stability and accuracy. Next the first portion of curve C is drawn, keeping its slope less than the maximum, and greater than the minimum, in the region below foot, to provide a signal adequate for accuracy purposes in this region. The remainder of curve C is extended from the first portion, either continuously or in steps, so as to join smoothly with curve B being careful not to exceed the maximum slope. It has been found feasible to make a smooth transition at a distance of approximately one foot by making the ordinates of curve C substantially equal to those of curve B in the region from one to two feet.

Potentiometer POTll (FIGURE 10) is constructed to have a non-linear resistance versus rotation characteristic on each side of its center tap in accordance with curve C of FIGURE 9, regarding the abscissa as degree of rotation and the ordinate as resistance. A one turn potentiometer has been found to be satisfactory for potentiometer POT 11 and may also be constructed by connecting suitable shunts across a plurality of taps. As in the case of potentiometer POT 10, voltages of opposite polarities V2+, V2 are connected to opposite extremities and the center tap is grounded. Potentiometer POT 11 may be connected in place of potentiometer POT 10 when the elevator car is anywhere in the region between one and two feet from the landing. Switching may be effected by switch SPDS which is operated in this region by shaft 694 through gear box XBl in the manner in which switch FSD is operated.

One effect of using curve C instead of curve B is that the time required to bring the car to the landing is increased. However, the increase is small because the variation from the prescribed operation to the desired one is slight and occurs only in the region below one foot.

It is obvious from the foregoing description of the invention that there are other arrangements by which the invention may be practiced. One such, which has been implemented but which at present is not as preferred as those previously described, replaces tachometer generator generator 34 and network 36 in the previously described embodiments with a device which produces a continuous indication of the load in the car and transduces that into a signal representing the heretofore defined load component of the hoisting motor armature current. This signal is then subtracted from a signal representing the armature terminal voltage to obtain a signal which is then fed back to summation network 30 to perform the same function as is performed in the previously described embodiment by the signals therein fed back to network 30.

From the foregoing description of the invention it can be seen also that there is provided a high gain elevator control servo system in which the speed of the hoist motor controlling the velocity of the car is varied in a continuous stepless fashion. In response to a starting signal, a device called a selector starts to scan the floors in advance of the car to select the next floor at which a stop is to be made. This enables a function generator of the system to generate a time controlled function representing desired speed characteristics of the hoist motor. This function is employed to cause a variable voltage source to provide excitation to the hoist motor. A stabilizing network together with a speed responsive signal source in the form of a tachometer provide feedback signals which are compared with the time controlled function to insure that the motor is operating in accordance with the desired speed characteristics. After the next floor at which the car is to stop is selected and when the car is a predetermined distance from the floor selected, a signal to stop is generated. This causes the time controlled function to vary its characteristics such that the variable voltage source changes the current of its excitation to the hoist motor and causes it to start to slow down. During this slowdown operation the variable voltage source is disconnected from the function generator and connected to the selector. In this way control of the variable voltage source is transferred from a time controlled function to a distance controlled one. The selector, thereafter, generates this distance controlled function to bring the car rapidly and accurately to rest at the selected floor.

It should be noted that this invention provides the same acceleration and retardation characteristics for both a full speed run and a less than full speed run. The only difference between these runs being the duration for which the car undergoes acceleration and deceleration.

It should also be apparent from the foregoing that once the desired speed characteristics of the elevator have been determined, the function generator and the selector can be designed and manufactured to provide these characteristics without the necessity of extensive field adjustments. Furthermore, it should be evident that the stabilizing network presents the only equipment which one might desire to adjust in the field.

Although the method of operation described is specific to particular magnitudes of acceleration, deceleration and jerk it should be appreciated that the invention is not limited to these magnitudes. Various other modifications are also possible, and it is intended that the embodiments specifically described not be considered to be exclusive or in any sense limiting.

What is claimed is:

1. A control system for controlling the speed of an elevator car which travels between floors in an installation in which the load in the car varies, in which the armature of a motor conducts a first current variable according to the load in the car to accelerate and t decelerate a plurality of members including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded a predetermined amount, and in which, when the load in the car does not balance the amount by which the counterweight outweighs the empty car, the armature conducts a variable second current to support the unbalanced portion of the heavier member and prevent it from falling undesirably, said system comprising:

a source of voltage of variable magnitude having an input circuit and an output circuit, said output circuit being connected to said motor to control the speed of said armature according to signals applied to said input circuit;

first means for generating a predetermined signal connected to said input circuit to apply said predetermined signal thereto;

and second means, including a speed responsive signal source responsive to the actual speed of said elevator car, connected to said input circuit to apply signals thereto indicative of the speed of said car;

said second means including circuitry connected from said armature to said input circuit and applying regulating signals thereto, said regulating signals being independent of the different steadystate magnitudes of said second current conducted in said arma ture to support said unbalanced portions and varying in magnitude for at least one condition of car loading proportion-ally and in synchronism with said first current conducted in said armature to accelerate and to decelerate said members so as to include a substantially synchronized miniature reproduction of said first current for at least said one condition of car loading.

2. A control system according to claim 1, wherein said first means includes a device for generating a predetermined signal variable as a function of the distance the elevator car is from a floor.

3. A control system according to claim 1, wherein said first means includes a function generator for generating a predetermined signal variable as a function of time.

4. A control system for operating an elevator car in an installation in which the load in the car varies and in which the armature of a motor drives a plurality of masses including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded a predetermined amount, said system comprising:

a source of voltage of variable magnitude having an input circuit and an output circuit, said output circuit being connected in said armature circuit to apply voltage thereto and to control the speed of said armature according to the magnitude of signals applied to said input circuit;

first means for generating a predetermined signal connected to said input circuit to apply said signal to said input circuit;

and second means, representing the resistance and inductance in said motor armature and also representing the inertia of said armature and the masses it drives, connected from said armature circuit to said input circuit to apply signals to said input circuit.

5. A control system for operating an elevator car in an installation in which the load in the car varies and in which the armature of a motor drives a plurality of masses including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded predetermined amount, said system comprising:

a source of voltage of variable magnitude having an input circuit and an output circuit, said output circuit being connected to said motor to apply voltage to said motor to control the speed of rotation of the armature according to signals applied to said input circuit;

a speed responsive signal source responsive to the speed of said car connected to said input circuit to provide signals, indicative of the actual speed of said car, to said input circuit;

means connected from the armature of said motor to said input circuit to provide signals to said input circuit, said means representing the resistance and inductance in said armature and also representing the inertia of said armature and the masses it drives;

and a device for generating a predetermined signal,

variable in a continuous stepless fashion as a function of the distance the elevator car is from a floor, connected to said input circuit to provide said predetermined signal thereto.

6. A control system for operating an elevator car in an instalaltion in which the load in the car varies and in which the armature of a motor drives a plurality of masses including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded a predetermined amount, said system comprising:

a source of voltage of variable magnitude having an input circuit and an output circuit, said output circuit being connected to said motor to apply voltage to said motor to control the speed of rotation of the armature according to the magnitude of signals applied to said input circuit;

a speed responsive signal source responsive to the speed of said car connected to said input circuit to apply signals, indicative of the actual speed of said car, to said input circuit;

a means connected from the armature of said motor to said input circuit to apply signals to said input circuit, said means representing the resistance and inductance in said armature and also representing the inertia of said armature and the masses it drives when the car is loaded said predetermined amount;

and a function generator for generating a pre-set signal, variable as a function of time in a continuous stepless fashion, connected to said input circuit to apply said pre-set signal thereto.

7. A control system for operating an elevator car in an installation in which the load in the car varies and in which the armature of a motor drives a plurality of masses including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded a predetermined amount, said system comprising:

a supply of single phase alternating current;

a plurality of silicon controlled rectifiers connected to said supply to conduct current from said sup ly;

a generator having an armature to apply voltage to said motor armature, said generator having a field connected to said silicon controlled rectifiers to be excited by the current conducted by said rectifiers;

first means connected to said rectifiers to control the portion of each cycle of said single hase alternating current supply during which said rectifiers conduct current;

second means connected from said generator field to said first means to alter the time constant of said field,

and third means, representing the resistance and in- 23 ductance in said motor armature and also representing the inertia of said motor armature and the masses it drives, connected from said motor armature circuit to said first means to regulate the excitation of said generator field.

8. A control system according to claim 7, wherein said third means includes a circuit having resistive, inductive and capacitive properties and whose resistive properties are representative of the resistance in said motor armature, whose inductive properties are representative of the inductance in said motor armature and whose capacitive properties are representative of the insertia of said motor armature and the masses it drives.

9. A control system for operating an elevator car in an installation in which the load in the car varies and in which the armature of a motor drives a plurality of masses including the elevator car and a counterweight heavy enough to balance the weight of the car when loaded a predetermined amount, said system comprising:

a supply of multi-phase alternating current;

a plurality of silicon controlled rectifiers, at least one rectifier associated with each phase of said multiphase alternating current supply, connected from said supply to said armature to conduct current to said motor armature from said supply;

first means connected to each of said rectifiers to control the portion of each cycle of the phase associated with each said rectifier during which each said rectifier conducts current;

and second means, representing the resistance and inductance in said motor armature and also representing the inertia of said motor armature and the masses it drives, connected from said motor armature to said first means to control the current conducted by said rectifiers.

10. A control system according to claim 9, wherein said second means includes a circuit having resistive, inductive, and capacitive properties and whose resistive properties are representative of the resistance in said motor armature, whose inductive properties are representative of the inductance in said motor armature and whose capacitive properties are representative of the inertia of said motor armature and the masses it drives.

11. A control system for an electric motor which is subjected to a variety of loads, said motor having a control winding for controlling the speed of its rotating element, said system comprising:

a source of voltage of variable magnitude having an input circuit and an output circuit, said output circuit being connected across the terminals of said control winding to apply voltages thereto to control the speed of said rotating element according to signals applied to said input circuit;

first means for generating a predetermined signal connected to said input circuit to apply said predetermined signal thereto;

a speed responsive signal source, responsive to the actual speeds of said rotating element, connected to said input circuit to apply signals thereto indicative of the speeds of said rotating element;

and second means connected to said input circuit for applying signals thereto indicative of derivatives of the speeds of said rotating element with respect to time, said second means including an electrical network connected across said control winding definable by a transfer function having one term which is a function of the inertia of the rotating element of the motor and the masses it drives when it is subjected to a predetermined one of its various loads, a second term which is a function of the inductance of the control winding of the motor, and a third term which is a function of the resistance of said control winding, whereby the current flowing through said network as a result of the terminal voltage applied across said control winding when the motor is subjected to said predetermined load is substantially a miniature reproduction of the acceleration component of the current flowing through said control windmg.

12. A control system according to claim 11, in which the motor is a direct current motor, the control winding is the armature winding of the motor and the speed responsive signal source is a tachometer generator coupled to the armature shaft of the motor.

13. A control system according to claim 12, in which the electrical network of said second means is an electrical analogue of the electromechanical system including the motor and the masses it drives when subjected to said predetermined load and in which said analogue includes a resistance, inductance and capacitance connected in a series circuit arrangement, the magnitude of the resistance being proportioned to the resistance in the motor armature, the magnitude of the inductance being proportioned to the inductance in the motor armature and the magnitude of the capacitance being proportioned to the inertia of the armature of the motor and the masses it drives with said predetermined load on the motor.

14. A control system according to claim 13, in which the product of the capacitance and inductance of said electrical network series circuit arrangement is substantially equal to the product of the magnitude of a capacitance equivalent to the inertia of the armature of the motor and the masses it drives at said predetermined load multiplied by the magnitude of the inductance in said motor armature.

15. A control system according to claim 14, in which the product of the capacitance and resistance of said electrical network series circuit arrangement is substantially equal to the product of the magnitude of the capacitance equivalent to the inertia of the armature of the motor and the masses it drives at said predetermined load multiplied by the magnitude of the resistance in said motor armature.

References Cited UNITED STATES PATENTS 2,629,847 2/1953 Eames et al 318- X 2,699,226 1/1955 Bruns 18729 2,858,493 10/1958 Hull et al 318146 X 2,918,987 12/1959 Haase et al. 18729 3,146,857 9/1964 Bosshard 187-29 3,155,891 ll/l964 Rosa 3l8--l45 X 3,297,110 1/1967 Bagnasco 18729 3,350,612 10/1967 Hansen et a1 318143 ORIS L. RADER, Primary Examiner.

W. E. DUNCANSON, 1a., Assistant Examiner. 

